A Southern California hospital says it has sent certified letters to 3,400 patients treated since Dec. 1, 2008 suggesting that they should consider returning for free tests for infection because endoscopic equipment used in their care may not have been properly disinfected.

“The 3,400 patients were identified and each received a certified letter,” says Andy Hoang, spokesman for Palomar Pomerado Health System, a public hospital district based in Escondido and Poway.